This invention relates generally to steam generators and processes for erecting steam generators. More particularly, the present invention relates to steam generators for thermal use of fossil fuels.
Today large steam generators are designed almost entirely as furnace wall steam generators. Their boiler wall is made as a furnace wall. The top part of the space enclosed by the boiler wall has interior components such as economizers, reheaters, superheaters, or other heat-exchange surfaces arranged in it. The boiler wall has buckstays and wall boxes on the outside, including headers arranged on cross-members. The lower end of the boiler wall has a boiler hopper attached to it. The entire boiler, including all the elements mentioned, is arranged so that it is suspended in a structural steelwork. The boiler structural steelwork, which stands on an appropriate foundation, has several boiler columns which are braced with one another by crossbeams and diagonal braces, and which bear a roof of the structural steelwork. The roof of the structural steelwork bears the boiler.
The steam generator is assembled at least partially at its installation site, which takes a relatively long time, due to the size of the plant and the scope of work. First the boiler structural steelwork, including the roof, is erected, after which the buckstays and, in the top part of the boiler, the boiler walls are brought from below to their installation site and installed there. The usual procedure then is for the interior components (heat recovery sections) also to be brought from below to their installation site between the boiler walls in the upper boiler area and installed there. Further assembly of the boiler wall is then done from top to bottom, with parallel assembly and assembly at different levels being mostly impossible. Therefore, the assembly of the upper boiler walls, the interior components, and the lower boiler walls is done in series, from the perspective of time. This is what determines the assembly time.
Concerning these problems, EP 0777080 B1 discloses a corresponding assembly process for steam generators, which involves beginning the assembly of the external boiler structural steelwork and a part of the boiler approximately simultaneously. Once the boiler structural steelwork has reached a certain minimum height, the boiler structural steelwork has hoisting equipment put into it to raise a roof of the structural steelwork, which up to then has been lying on the floor (base of structural steelwork), first to a first height. At this height the boiler components are assembled suspended below the boiler structural steelwork. As the building of the external boiler structural steelwork progresses, the hoisting equipment is moved upward and the roof of the boiler structural steelwork is also raised further, to make possible further assembly of the heat exchanger surfaces. After the boiler structural steelwork is completed, the boiler part suspended from the roof of the boiler structural steelwork that has been simultaneously assembled in this manner is raised upward, and the roof is attached to the boiler structural steelwork.
The boiler walls and interior components can only be assembled one after the other in time.
Starting from the above-described state of the art, it is the task of the invention to reduce the building time for steam generators.
This task is solved by the assembly process according to claim 1. Moreover, the task is solved with a steam generator according to claim 11, which allows a shortened building time.
The process according to the invention for assembling steam generators involves building interior components, such as economizers, superheaters, and similar heat recovery sections during the construction of the upper boiler wall at a location that is at a distance from the installation site. Therefore, they can be assembled simultaneously. The spatial distance allows each part of the assembly work to be carried out largely unimpeded. This temporally parallel way of working can save substantial building time. In the process, the boiler walls are assembled or installed at their final installation site.
A preferred embodiment involves first erecting only an outer part of the roof on the boiler structural steelwork. This outer part leaves an access opening free in the middle, which preferably is smaller than a horizontal section through the boiler. The crane can feed elements belonging to the upper part of the boiler wall, such as buckstays, wall boxes, and tube registers through this access opening to their respective installation sites. The lower part of the boiler structural steelwork and the boiler base are not needed for this purpose, so they are kept clear.
Accordingly, the boiler containing walls are erected, for example, by using a crane to raise individual buckstays and wall boxes, or buckstays and wall boxes that are preassembled, into the boiler structural steelwork, and suspending them there temporarily on the roof of the boiler structural steelwork or temporarily storing them in corresponding intermediate storage locations. Alternatively, the buckstays can be built at the same time that the upper part of the boiler structural steelwork is built.
After the buckstays and any possible wall boxes are assembled, tube registers for building the boiler wall can be raised from above by a crane into the inside space that is surrounded by the buckstays. Then, the tube registers are fastened to the roof of the boiler structural steelwork so that they are suspended, and they are welded together with one another. Furthermore, other connections can be made, e.g., to the buckstays and wall boxes.
While the individual buckstays, wall boxes, and tube registers are assembled in the upper boiler structural steelwork, an inner section of the roof of the boiler structural steelwork is built and/or kept ready on the base of the boiler structural steelwork. The outer section of the roof of the boiler structural steelwork also has hoisting equipment, for example a cable hoisting system, erected on it, whose traction mechanisms (cables) are connected with corresponding suspended parts of the inner roof section. In this preferred process variant, the preassembly of the boiler top casing as well as the assembly of the interior components (tubular coils for economizers, reheaters, and superheaters) takes place suspended under the inner section of the roof of the boiler structural steelwork. In the process, the interior components are anchored with sling tubes under the roof of the boiler structural steelwork so that they are suspended from it. Thus, simultaneously with the erection of the boiler walls of the upper area of the boiler, a structural unit is constructed from the roof of the boiler structural steelwork, the boiler top casing, and the interior components. The cable hoisting system can then be used to raise the inner section of the roof of the boiler structural steelwork step by step, each time far enough so that each next unit from top to bottom can be assembled. After partial assembly, all that then remains is to raise this unit by means of the cable hoisting system until the interior components reach their installation position and the inner roof section is raised to the height of the roof of the boiler structural steelwork. After the spatially separated but simultaneous assembly of the upper boiler wall and the interior components, the two are united by raising the interior components from below.
Thus, the two building site areas for the upper boiler wall and the interior components are arranged vertically above one another, separate from one another, and at a distance from one another. The boiler structural steelwork roof is divided into an outer roof section and an inner roof section. The outer section of the roof of the boiler structural steelwork bears the boiler walls with their buckstays and wall boxes, as well as the inner section of the roof of the boiler structural steelwork. The inner roof section in turn bears, through corresponding sling tubes, the interior components of the boiler. The outer roof section is assigned to the boiler structural steelwork and the boiler walls. The inner roof section is assigned to the interior components.
This assembly process is suitable both for once-through steam generators and for recirculating steam generators. It is also suitable both for boiler walls with vertical tube arrangements and for steam generators with inclined tube arrangements or for steam generators whose boiler walls have vertical and inclined tube arrangements. The assembly time of the steam generator can be shortened by several months.
For preassembly of the interior components, it is preferable to raise the inner section of the roof of the boiler structural steelwork in a stepwise manner to make it possible to assemble, in top to bottom sequence, the various interior components and correspondingly also their sling tubes. This makes it possible to erect several economizer heating coils, reheater heating coils, and superheater heating coils in a stepwise manner above one another. The spatial separation of the building sites of the top boiler walls and the interior components brings not only a gain in time, but also a substantial improvement in the assembly logistics. Feeding the parts of the top boiler wall from above means that the base of the structural steelwork remains clear for building the interior components.
The steam generator according to the invention has a divided roof of the boiler structural steelwork. Its inner roof section is dimensioned such that it, together with interior components that are suspended from it, can be moved through the inside space bordered by the boiler walls. Thus, the outside dimensions of the inner section of the roof of the boiler structural steelwork are smaller than the cross section of the space enclosed by the boiler walls. The same goes for the interior components such as economizers, reheaters, and superheaters. For this purpose, it is preferable for them to have assembly connections which lie inside the space enclosed by the boiler walls. It is preferable for assembly to be done by welding to wall penetrations or joining pipes.
The inner section of the roof of the boiler structural steelwork forms, together with the interior components that are mounted to it and possibly a boiler top casing, a preassembled subassembly. It is then possible to put it as a whole between the already assembled furnace walls and into its installation site and connect it there. This manner of building has substantial assembly advantages, since it allows simultaneous assembly or preassembly of the boiler containing walls and the interior components at separate locations.
When the building of the steam generator has been completed, the inner roof section is connected with the outer roof section. This can be done with bolt connections, or it can also be done with non-detachable means of connection, such as rivets and welding connections.
The boiler structural steelwork and/or the outer section of the roof of the boiler structural steelwork can have hoisting equipment on it if necessary, and it can be temporary. It then forms a hoisting system to raise the inner section of the roof of the boiler structural steelwork in steps during preassembly, until all interior components have been suspended from the inner section of the roof of the boiler structural steelwork. After that, the hoisting system can be used to raise the subassembly that has been preassembled in this manner to its installation site and keep it there until other means hold the structural unit in its location and, for example, the inner roof section is connected with the outer roof section.
After this assembly step, the hoisting system can be removed, if necessary. The hoisting system can work either by pulling from above or by pushing from below. Furthermore, several hoisting system can work together.
Other objects and advantages of the invention will become apparent from the drawings and specification.